High performance blocking electrode for electrophotophoresis

ABSTRACT

Compositions suited for use as a blocking electrode material in a photoelectrophoretic imaging process are disclosed. These compositions comprise a mixture of a polymeric material and a finely divided ferroelectric filler such as a metal titanate or stannate. Blocking electrodes so prepared exhibit the high dielectric constant and high dielectric strength which are desirable in a blocking electrode.

United States Patent 1191 Sheckler et a1.

[ Jan. 7, 1975 [5 HIGH PERFORMANCE BLOCKING 3,744,896 7/1973 Carreira 355/3 P ELECTRODE d 3,776,628 12/1973 Gundlach 355/3 P ELECTROPHOTOPHORESIS Inventors: Addison C/Sheckler, Cato; Luke C.

Lin, Rochester, both of N.Y.

Assignee: Xerox Corporation, Stamford,

Conn.

Filed: Feb. 15, 1973 Appl. No.: 332,974

US. Cl. 317/262 A, 204/300, 355/3 P Int. Cl. H011 19/00 Field of Search 204/280, 299, 300;

[56] References Cited UNITED STATES PATENTS 3,551,320 12/1970 Krieger et al 317/262 Primary Examiner-.I. D. Miller Assistant ExaminerHarry E. Moose, Jr.

ABSTRACT 15 Claims, 4 Drawing Figures ,ticular, to photoelectrophoretic imaging-systems eni ,ploying novel blocking electrodes.

I Whie the blocking electrode is subject to cyclic HIGH, PERFORMANCE BLOCKING ELECTRODE r FORELECTROPHOTOPHORESIS renseas, for example, in the embodiment shown in I. FIG. 1, the resistivity of the blocking layer should not BACKGROUND OF'THE INVENTION The invention relates to imaging systems and, in par ,ln the,photoelectrophoretic imaging process, an mechanical strength, solvent resistance, and compliiniage is'formed from an imaging suspension or ink by ,ance are' often at odds with one another. For example,

subjecting the ink toahelectricfi'eldand g g liposingit to some materials such as elastomers and plastics may activating electromagnetic radiation,'e.g.j?light in the possess requisite high dielectric strength and mechani- -visible spectrum. The ima'gingsushension is composed cal properties,.but have a low dielectric constant, gen- Of light sensitiveparticles suspended within an insulaterally in the orderof less than eight or a resistivity in ing liquid carrier. The parltii-Eles are believed to bear a excess of that desired in a blocking material used in a net elect ricalcharge'while in suspension and during imcycle process. On the other hand, a material such as aging. Conventionally,the ink is placed between elec- Baryta paper, which consists of paper coated with bartrodes used 'toles t ablish the electric field and is'exposed ium sulfate suspended in a gelatin solution, leaves toalighfiniage throughone of the electrodeswhich is something to be desired in terms of mechanical at lea tp 'artially transparent. According to one theory, strength, compliance and durability.

paiggcles attracted to the transparent injecting elec- Accordingly, it is a primary Object of this invention t de by the electric field exchange charge, directlyor to define a blocking electrode incorporating the above indirectly, with the injecting electrode when exposed to and other advantageous chemical, mechanical and light, and migrate under the influence of the field "electricalproperties. through the liquid carrier toward the opposite elec- Yet another object of the invention is the enhancetrode. As a-resultof the'migration, positive and nega- I ment of the photoelectrophoretic process. tive images are formedon the two electrodes. A specific object of this invention is to build a block- I The photoelectrophoretic imaging process is either. ing electrode-having a polymeric blocking layer having herein by reference and loss of imagequalityQne-method*oflovercoming' monochromatic or polychromatic, 'depending upon good compliance, high dielectric strength, high dielecwhether the light sensitive particles within the liquid tric constant and relatively short time constant. carrier are responsive to the'sameor different portions 1 Another object of the present invention is to develop of the light spectrumfA-full color polychro matic sysf embodiment'sof the photoelect'rophoretic process that tem is obtained, for example, by using cyan, magenta tend to optimize the parametersand/or overcome the and yellow colored particleswhich areresponsive to limitations of the blocking electrode.

red, reen and blue light;'rspectively. An extensive y and detailed d'escriptionpfthe photoelectroph oretic Y U A Y OF T INVENTON process is found in 'UIS. Pat. -No'si 3,384,565 and i The foregoing and other objects of the invention are 3,384,484 to Tulagin and Carreir'a 3,383,993to Yeh realized by preparing blocking electrode material comand 3,384,566 to Clark, all'of whichjareincorporated 5 prising apolyrneriomatrixj material having incorpo- -f f. rated therein effective amounts ofa finely divided fer- A high field between the electrodes isrequired for 1 'roelectric materialjor a'mixture offerroelectric materi efficient imaging. However,'a highfield increases the alslsufficient to enhance the electrical properties of the possibility of dielectric breakdown of the imagingsus polymeric materialforuse in an electrophoretic imagpension, possible damage to "the injecting, electrode, ing process..'Preferredferroelectrics are those materials having a dielectric constant of from about l5 to 10,000

this problem is to in'terpo'se alayer. of high resistivity 1 (10He'rtz) or more f'such as alkaline earth metal titamaterial, i.e., greater than about l0"'ohrn'- cr n,".between .,'natesfor stannates, More preferred are ferr'oelectrics 'the imaging suspension on the injectingelectrode and h aivinga dielectric constant in excess of about "100,

-terial in association with the conductivesupport which u 7 forms the electrode oppositethe injecting elfectrodeis 'entinventionmay. bejin the form of a conductive'roller' the opposite electrode. This laye r'ofhigh resistivity na-li' such as barium or strontium titanate. The blocking "electrode encompassing the blocking layer of the 'presknown as the blocking electrode. The blocking elecc on'nect'ed to a source of'potential and having a film of 1 trode functions as a current limiting device and prethe blocking layer adheredto its surface, as in FIGS. 1 l

' and 2. The blocking electrode may also be in the form vents significant charge'exchange between it andthe particles ofthe ink suspension which havernig'ratedto its surface during the imaging process.

' connectedto a source of potential underlying a layer of of an endless belticomprising a conductive material Besides being of the requisite resistivity, the blocking :the blockirig material, as in FlGl 3rTheblocking eleclayer must also be able to withstand-a high electric flux trode may also take the form ofa web comprising a density generated during the imaging process. For-best roll-fed sheet of the blocking material which is superresults'in terms of image quality, a highelectric field imposed between an injecting electrode and a conducordinarily in the orderof greater than 10 volts per tive backingelectrode, an embodiment of which is meter is generated in the ink. Thus, during imaging if I shown" in FlG. 4.

theblocking layer-and inksystem were to be regarded Where thepolymeric blocking material containing as two resistance/capacitance circuits in series,' itis inithe-ferroelectric exhibits'a volume resistivity in excess portant that the dielectric breakdown strength and di- I of about l0} ohmcm and is intended for use In a conelectric constant of the blocking layer be sufficiently 'tinuous process involving continuous cyclic exposure high to support the high field generated. I of the same' 'surface to'th'e imaging process as in FIG.

.lifor example ithas been found thatthe electrical properties of the blocking material may be further enhanced by additionally including minor amounts of a material more conductive than the polymeric material used in fabricating the blocking laye'r. Examples of suitablematerials are graphite, conductive carbon black,

' Lewis acids, plasticizers, polyelectrolytic resins and the Alternatively, the polymeric blocking layer may be fabricated into a web or sheet adapted to be fed into intimate contact with a conductive substrate.

DETAILED DESCRIPTION OF THE DRAWINGS Other-objects and features of the present invention will become apparent uponthe reading of the .present disclosure and from the drawings whichillustrate several ofthe environments in which the polymeric blocking-layers of this invention are used.

FIGS. 1 and 2 are schematic sidesectional views of- DETAILED DESCRIPTION OF INVENTION In order to more thoroughly understand the role of the blocking electrode material of this invention in photoelectrophoretic imaging processes, a discussion of several exemplary systems is warranted.

Referring now to FIG.']., there is seen a, transparent electrode generally designated as 11 which'in this case is made up of a layer of optically transparent glass '12 overcoated witha thin optically transparent layer l3'of tin oxide. This oxide coated glassis commercially available under the trade name NESA glass from Pittsburgh Plate Glass Company, Pittsburgh, Pa. This base electrode is referred to as the injecting electrode. Coated on thelayer of electrode 1 1 is a thin layer of finely divided photosensitive particles dispersed in an insulating carrier liquid. This suspension 14 may also contain sensitizers and/or binders for the particles which are dissolvedor suspended in the carrier liquid along with the particles. Adjacent electrode 11' is a roller electrode 23 which is connected to one side of a potential source 17 through a switch 18 with the opposite side of the potential source being connected to the tin oxide-coatingon electrode 11 so that when switch 18 is closed an electric field is applied across the liquid suspension as electrode 23 rolls'across the surface of electrode 11 in the direction indicated by the arrow in the drawing'Electrode 23 is made up of a central core 24 which is preferably of fairly high electrical conductivity and is cov. ered with a layer of blocking electrode material 26. An image projector made up of light source 19, a transparency 21 and a lens 22 is provided to exposed suspension 14 to a light image of the original transparency 21 4 to be reproduced. In-imaging the roller :23 is caused to roll across the top surface of electrode 1 1- with switch 18 closed during the period of exposure. This exposure causes exposed particles originally on electrode 11 to migrate through the liquid and adhere to the surface of the blockingelectrode leaving behind a particle image on theinjecting electrode surface'which is a duplicate of the original transparency 19. This image may then be fixed in place as, for example, by placing a lamination 'over its topsurface or byvirtue of a dissolved binder material in the carrier liquid such as a paraffin wax or other suitable binder that comes out of solution as the carrier liquid evaporates. In fact, the carrier liquid itself may be a molten paraffin wax or other suitable binder ina liquid state which is self-fixing upon cooling and return to the solid state. In the alternative, the particle image remaining on the electrode 11 maybe transferred to another surface and fixed thereon, if desired. The system has been found to be capable-of producing either'monochromatic or polychromatic images depending upon the color, sensitivity and number of different pigments suspended in the carrierliquid and the color light to which the suspension is exposed.

In FIG. 2 there is shown anapparatus whereby a large broad area tracking contact is made by the blocking electrode with the imaging suspension 14 during the imaging process. Like numerals have been used to identify like elements throughout FIGS. 2 to 4 where they correspond with the elements of the FIG. 1 device, and as can be seen from FIG. 2, this device is identical with that of. FIG. 1 with the exception of the blocking electrode structure wherein a roller, generally designated 29, isemployed. This roller electrode 29 consists of a very soft central core 31 which may be of fairly high electrical conductivity. If a low conductivity material'is used, a separate electrical connection is made to the backof blocking layer 32. This core is coated with a blocking electrode material 32. The blocking electrodelayer may be a separate replaceable layer which is either taped on the roller or held by mechanical fasteners or any other device which is capable of releasably holding the layer on the roller; or in the alternative the layer may be-integral with the roller itself, being either adhesively bonded, laminated, spray coated or the like on the surface of the roller. It is important that during passage of roller 29 over electrode 11 the two be held together with sufficient forceso that the roller material is compressed to provide a flat large area contact between the roller and the electrode 11.

.In FIGS. 3 and 4, two additional embodiments are illustrated except that the image projector has been left out of these figures to simplify the illustration. In the FIG. 3 embodiment the same NESA glass electrode 11 with a coating of the imaging suspension 14 thereon is employedand is connectedto a potential source 17 througha switch l8as in the previous figures. The other side .of potential source 17 is, however, connected to apair of rollers 36 and 37 and a hold down platen 38.within an elongated endless belt blocking uniformly from this layer through the imaging suspension as the belt passes over electrode 11.

As with the central core 31 of roller 29, the substrate 41 of belt- 39 may, for example, consist of any suitable material of relatively conductivity. Typical a I cause electrode l'l to make the desired contact. Hold down platen 38 may also be replaced with a plurality of rollers if-desiredso a'sto reduce friction while still pressingthe belt surface downwardlyduring its passage over. electrode l1.v Other-modifications of the apparatus which willalsoproducea tracking contact of the .endless belt-'39 over electrode'll' will occur to those skilled in the art.Thus, for example;lthe two rollers and ';hold down platen mayall bereplaced with a reinforced block of material having a low'coefficient of friction i and having the shape a'sdef ned by;the inside of thebelt was-seen in FIG. -3, and this block with the belt on its outer surface may simply be slid across electrode 11 so that thesame type of tracking is'caused to occur. Rotation of the belt in this instance would be caused by the frictional contactof'the"outerjsurface of thebelt with electrode 11 and the low degree of frictional drag ber tween the belt and the block whichwould tend to restrict its rotation around the'block, In another modification the rollers may be providedwithteethrunning parallel to their axes adapted to jen gage' ridges cut into the innersurface of the belt soas to provide a positive drive forthe belt itself as it tracks-over the electrode. Referring now to FIG. 4', there'is see n a third embodiment in which the blocking electrode is supplied in the I form of an. elongated web 44 provided from a supply are all journaled for rotation on. a mouhting plate49;

A similar mounting plate "may also bepi ovidedat'the near end of the'se r'eels and rollers;- a's'jseen in;FlG 4, so

that they will be journaled at-both endshsogas to make up a rigid carriage frame for 'the'wholeblocking' electrode assembly. In operation, this assembly is'moved so electrode oyer'electrode ll.

in US. Pat. Nos. 3,565,614 anal-609,028.

The blocking electrodelmaterial which is the subject. j matter of the present invention is shwonin an imaging apparatus environment at 2 6 in FIG 1; 32 in FIG. 2; 42- {in FIG. 3; and 44,in*FlG. -'4.

i As indicatedabove, the blocking electrode material f of this invention is-prepared from a-compositioncom-f prising a polymeric material having dispersedtherein a finelydividedferroelectric material. The term poly; meric is intended toencompa'sselastomeric polymers such as natural or'synthetic rubber, thermoplastic res ins and blends thereof, said polymeric 'materialha'ving' a volume resistivity of at least about 10 ohm-cm at ductivematerialsare conductive rubber, metal foils of steel; aluminum, copper, brass or the' like, Blocking electrode layer 42 overlies substrate 41. Rollers 36 and 37 and hold down platen 38 may all be mounted on the 1 same carriage so that movement of the carriage in the direction indicated by the arrowin the drawing will 23C. The particular polymer to be used will depend primarily on the demands to be made upon the block- 'in'g electrode during the imaging process and the type of apparatusin which the blocking electrode is employed. Where the blocking electrode material is to be used once and then discarded, as could be the case in the scheme of FIG. 4, virtually any polymeric material I which can be formed into a sheet or web and which ex- .hibits structural integrity under operating conditions mayib'e used. Exemplary of such materials would be polyolefins such as polyethylene or polypropylene, chlorinated and chlorosulfonated polyolefins, polyacrylates, polyvinyl halides, vinylaromatic polymers such'as polystyrene, diene polymers such as natural rubber,'polybutadiene, polychloroprene, butyl rubber and ethylene/propylene/diene terpolymers, polyurethanes, polyesters", polyethers and the like. Copolymers of monomers from which the above polymers are derived may also be employed. Where diene or rubbery polymers are used, they should be in'the cured state. Best results in terms of image quality are achieved 'using polymers which, when cast into a sheet or web,

exhibit good compliance and flexibility. These characteristics are inherent in elastomeric polymers and can be imparted into more brittle polymers by the use of scheme of FIGS. 1, 2 and possibly 3, polymers meeting more stringent requirements in terms of their mechani cal and chemical properties should be employed. Good solvent resistance an d'resistance to abrasion and oxidation are important because of continuous exposure. to air and'solvents contained in the photoelectrophoretic ink. In addition, the polymer used'in formingthe blocking layer of the roller electrode as in the scheme of FIG.

should be quite compliant was to assume as nearly [as possible the shape of the surface oftheinjecting 'electrode'as'it' rolls across the surfacejof the electrode.

Exemplary polymers particularly" meeting the above criteria in varying degrees are cured elastomers com- .prising polyepihalohydrin, copolymers of epihalohy- I ,.driri with ethylene oxide, polysulfide rubber, silicone as to track the blocking electrode 44 over electrode-11 t by following path 5lshown in the figure in dottedlineL In this way, the blocking-electrode web'44 willtrack I over electrode 11, be lifted up. and -'return;baek to its original position so that}; new section ofblockingielectrode material willT-bef lprovided.for eachpass'. ofl'thisj j'w" rubber, dioletin/acrylonitrile copolymers, polyacrylic r'ubbe r and like materials and blends thereof.

-.A second component of'the blocking layer of this in- V ven tion comprises-a finely divided ferroelect ric matea rial uniformly dispersed .in the polymeric matrix. This The above apparatus a d processes are morei'thormaterial function's primarily to increase the dielectric oughly described in U.S."Pat. No. 3,55 l ,320.-E xamp lesj t t con tantIOfthepolymeric layerlthereby enhancing the of other photoelectrophore't'ic apparatus maybe found ability of'the. polymer to support the high electric field andhigh flux density generatedduring the imaging processtlt-has' been found in actual practice that suitable V "results iinthe electrophoreti'c imaging process are ob-- *tained-when the blocking layer exhibits. a dielectric constant of at least about'eight. Optimum results are achieved when the dielectric constant of the blocking layer is at least about '15, preferably from about 30 to about 9Qor moreQThis is accomplished according to The term ferroelectric material as used herein is intended to referto those materials having a dielectric constant in excess of 1 5 Hertz) and preferably within the range of from about 100 to 12,000. Exemplary of preferred material are metal titan'ates and stannates, specifically the alkaline-earth metal titanates and stannates. v The amount of ferroelectric material blended with the polymeric material will vary as a factor of the dielectric constant of the particular polymer employed and the'dielectric constant of the'ferroelectric. Most polymers have a dielectric constant within the range of about 2 to about 7. More of the ferroelectric is required where the polymer has a low initial dielectric constant. lngeneral, from about to about 90 percent by weight ferroelectric based on polymeric material has been found sufficient to increase the'dielectric constant of the polymer-composition to'withinthe acceptable range. In most'cases, a loading of about 50 to 85 percent by weight of the ferroelectric is required in order ,to impart an optimum dielectric constant of about 30 to 90 into the polymer composition.

The polymeric material and the ferroelectric material may be mixed by any convenient method. The ferroelectric is preferably used in finely divided form, i.e., an average particle size within the range of about 0.1 to 10 microns. Blends may be formed by adding the powdered ferroelectric to a hot melt of the polymeric material in a mill mixer such as a Brabender Plastograph. Mixing may also be carried out using a Banbury mixer which is commonly used in rubber compounding, or by mixing the powder with a polymer latex prior to coagulation and recovery of the latex. Where the polymeric material comprises an elastomer which is to be cured or vulcanized, the appropriate'curing agents and rubber processing aids as are known in the art may also be added at this time.

Although blocking electrodes having'a blocking layer prepared from the mixture of polymeric material and ferroelectric perform quite well in the electrophoretic process, certain problems may arise where the blocking electrode is intended for use in a continuous process involving cyclic reexposure of the same surface to the high imaging field, as would be the case where the electrode is in the form of a roller as-in FIGS. 1 and 2. Re-

sidual charge present on the surface of the electrode from a previous cycle must be substantially dissipated before a second cycle commences or the residual charge will interfere with subsequent imaging'ln other words, the blocking layer should have a relatively short time constant or relaxation time which should be less than the cycling time but greater than the imaging time. For the purposes of this invention, it has been found thatthe volume resistivity (23C) of the blocking layer should be less than about 10 ohm-cm, preferably wtihin the range of about 10 to 10' ohm-cm, in order for the blocking layer to sufficiently self-discharge residual charges via internal conduction between the use cycles. Thus, where the volume resistivity of the blocking layer comprising the mixture of polymeric material and ferroelectric material is in excess of 10' ohm-cm and the blocking layer is intended for cyclic reuse, the'volume resistivity may be lowered to within acceptable limits by intimately mixing with the blocking layer composition minor amounts of an additive which is more conductive than the polymeric material. Exemplary materials suitable for this purpose include conductive fillers such as graphite and conductive carbon black, Lewis acids, polyelectrolytic resins such as O 26l 1.12 which is'a polyquaternary ammonium salt complex available from Dow Chemical Co., plasticizers such as triphenyl or tricresyl phosphate or N-ethyl p-toluenesulphonamide, polymer curing agents, and impurities such as organic dyes and halogen molecules. In general, the conductive additive should have a volume resistivity of less than 10 ohm-cm (23C) and preferably'less than 10 ohm-cm, and may be used at alevel of'from about 0.1 to about25 percent by weight, based on the weight of polymeric material. t

The above compositions may be fabricated into a blocking layer for use in conjunction with a blocking electrode by any one of a number of techniques'The polymeric blocking layer may be applied to the appropriate conductive substrate directly by dip or roller coating. Alternatively, sheetsor films of=the polymeric materials may be prepared by casting films or by compression molding, and these applied to the substrate by adhesive lamination or by heat shrinking where the polymeric material is one susceptible to heat shrinkage. Where the polymeric material is an elastomer which is to be cured prior to use as a blocking layer, the elastomer containing the appropriate curing agents may be cured in situ after application to the conductive substrate, or films and sheets of the elastomer may be formed, cured and subsequently applied to the conductive substrate. In another embodiment, the polymeric blocking layer may be fabricated into a web or sheet which is adapted to be fed into ultimate contact with a conductive substrate during the imaging process. These webs or sheets may be prepared by continuous film casting processes, extrusion, solvent deposition and like techniquesknown to those skilled in the art. Webs and sheets may also be preparedby forming a thin continuous coating of the polymeric composition on a relatively inert substrate such as paper or by saturating a loose matrix such as paper prior to calendering.

The thickness of the blocking layer may vary within wide limits, but shouldbe substantially uniform for best results. The minimum thickness is determined by practical considerations such as the particle size of the various additives present in the blocking layer composition and the ability to cast uniform films without the forma* tion of irregularities or pinholes. The upper limit of film thickness is limiting in the sense that the total potential established between the injection and blocking electrodes must be maintained by increasing the voltage as a function of the thickness of the blocking layer. For the purposes of this invention the substantially uniform thickness of the blocking layer should be at least 1 mil, preferably. within the range of about-5 mils to about one-fourth inch, and more preferably within the range of about 10 to mils.

The conductive support underlying the blocking layer may comprise any suitably conductive material such as metal or conductive rubber, or a sleeve of conductive rubber overlying a metal core. The conductive support in turn is connected to a source of potential. Where the blocking electrode is in the form of a roller as in FIGS. 1 and 2, the use of conductive rubber imparts added compliance to the roller electrode.

The following examples are illustrative of compositions suitable forv use as a blocking layer and methods for preparing them.

Examiner a The following materials were mixed and compounded on a rubber mill:

Parts by Weight A cured film comprising the above composition having a thickness of about 25 mils was prepared by curing the composition in'amold in a hydraulic press at 350F for 20 15 minutes. The cured film exhibited a dielectric constant of about 15 anda volume resistivity in theorder. of 10 ohm-cm.

The film was bonded to a conductive roller substrate like that shownatf'24' in FIG, 1 having a diameter of about 4 inches and ail'engthof about 12 inches. Excellent images were produced using this assembly as the blocking electrode. r

EX MPLE 1] 2' The following materiaIsiwere mixed and cornpounded on a rubbermill: 5

i Parts by Wei ht Polyepichlorohydrin v f I, I k

v (Hydrin 100) 100.0. Magnesium stearate 1.0 Lead phosphate (dibasic) 7.5 Hexamethyldiamine carbamate 0.8 Phenol salicylate powder 0. Barium titanate powder 300.00

A cured film having a thickness'ofabout20 milsiwas prepared by curing the composition-ina hydraulic press at 280F for one 'hour. The filmexhibited adiele'ctric. constant of about, 60 and'a resistivity of about ohm-cm. I

A blocking electrode similar to that shown in FlG. 3

The film exhibited a dielectric constant of about 70 and a resistivity of about 10 ohm-cm. The N,N-mphenylene dirnaleimide functions. in this formula both as a curing aid and a conductive material. Without this material, a resistivity in the order of 10 ohm-cm would be expected.

EXAMPLE IV A filmfhaving a thickness of about mils was prepared bycompounding and curing the following composition as in Example 11:

Parts by Weight Chlorosulphonated poly 'ethylene 400 Polyepichlorohydrin 60.0 Magnesium oxide 4.0 Zinc oxide 1.0

Barium/cadmium soap (Ferro 1827) 2.0 Barium titanate powder 280.0 Z-mercaptoimidazoline 1.2

. N,N-m-phenylene dim'aleimide 0.6

is constructed by laminating a lehgith ioftfilmprepared. i

as above 42 to a inch thick beltcomfprising conductive rubber 41 containing.a-highI'loadingof carbon black. As in Example 1. the, blocking electrode pro duced excellent images 'when us'ed injth'e electroph retic imaging process.

. EXAM FILE 111;

A film having a thickness or about 2'0 rn'ils and exhibiting excellent imagingcharacteristics when-{used as a blocking layer in a blockinge'lect rod e was-prepared by compounding and curing the following compo'sitionas in Example 11:

karts by Weig ht Chlorosulphonat'e poly- V V Y ethylene (Dupom Hypalon) 100.0 Litharge I 25.0 Dipentamethylene thiuramtetrasulfide' -l.'0, N,N-n1-phenylene dimaleimide 1.0 300.9 v

Barium titanate powder Polyurethane resin* Mercaptobenzothiazyl disulfide The film exhibited a dielectric constant of about and a resistivity of about 10" ohm cm.

EXAMPLE v e In this example, carbon black is used to lower the volume resistivity of the composition to less than 10 ohm-cm. A film having a thickness of about 25 mils was prepared by compounding and curing the following composition as in Example ll:

Parts by Weight Chlorosulphonated polyethylene l0 Magnesium oxide Barium titanate powder Dipentamethylene thiuramtetrasulfide 5 o OMLA Carbon black 7 2 Epoxy resin (Epon 828 Shell Chemical Co.) V 4 This film produced excellent imaging when used in conjunction with a roller electrode as in Example 1.

EXAMPLE V1 The following ingredients were dispersed in cello- 'solve acetate solvent at about 35 percent by weight solids: A v v Parts by Weight I w 25.0 Strontiumtitanateff 75.0

Chemglaze Hughson Chemical Company f'f -Na'tional Lead Company j Specific gravity 4.81 V jBulk density 84 Melting point 7340F Fineness 0.563 microns j Dielectric constant "(10 Hertz) 225-250 The dispersion was sprayed evenly onthe surface of a stainless steel roller electrode similar to that shown in FIG. 1 in amounts sufficient to forma coating having [a dried film thickness of about 2 mils. The film exhibited a dielectric constant of about 9 and a resistivity of about 10 ohm-cm. The resultant blocking electrode produced a good image when subjected to single cycle imaging in the electrophoretic imaging process.

he" I imaging.process-mafialso be prepared from blends comprising a mixture ofthermoplastic material such as 'polymethylmethacryilate, polystyrene, polyvinyl fluoride, polyvinylidenef -fluoride, polyethylene, polypropylene and the like-a d from about 20 to 90 percent by weight of finely lvided ferroelectric material such as barium titanat e r strontium titanate. These compositions may be, applied in thicknesses ranging from about 1 mil to (vi nch by spraying, dipping or roller coating to any suitable substrate such as the conductive roller 24 of filG. l, the conductive roller 31 of FIG. 2, or conbelt 41 of FIG. 3. Alternatively, the composindicated at 44 of FIG. 4, What we claim is:

phoretic imaging process comprising:

' a. a conductive support having means for coupling to 1. A blocking electrode for use in a photoelectro- I 1. i M Suita'ble blockinglaygi s for use in the electrophoretic 8. The blocking electrode of claim 7 wherein the polymeric layer further contains from about 0.l to about 25 percent by weight of a conductive material having a volume resistivity of less than about 10 ohm- 9. The blocking electrode of claim 8 wherein said conductive material comprises carbon black. 10. The blockingelectrode of claim 6 wherein the cured elastomer is selected from the group consisting of butadiene/acrylonitrile rubber, chlorosulfonated polyethylene, epichlorohydrin polymers and mixtures I a polymeric layer contact with said conductive 2. The blocking electrode of claim-l-wherein *said polymeric layer is adapted for interpositionbetween' the conductive support and a second electrode.

3. The blocking electrode of claim 2 wherein said feir -T roelectric material is selected from the group consisting of alkaline earth metal titanates metal stannates.

4. The blocking electrode of claim 3;,whe'reih said and alkaline earth polymeric layer is in the form'of a sheet adaptedffor feeding between said conductive support ,and "said ega? 0nd electrode."

s. The blocking electrode of claim" 13" wheels cello;

conductive support comprises a cylinder or continuous 7. They blocking electrode: of claim 6 wherein/said polymeric layer has a dielectric constanteof at least; about 15' and a volume resistivity within therangeof about lOto lol -ohm-cm.

meric' layer being at least about 5 mils. 7- 14. The l'alocking"v layer of claim 13 wherein saidpoly- I ne'r ic materialisa c'uredelastomer selected from the groupj'consisting-Kofgbutadiene/acrylonitrile rubb'er," fchloro jsulfonated polyethylene, epichlorohydrin polysupport and interposed between said conductive support and a secondelectrode;

said polymeric layer comprising a v uniform'mixture of a' polymeric materialhaving a volume resistivity of greater-than about 1.0 ohm-cm and-a finely divided ferroelectric materialselected from the group con sisting of barium titanate, stro'ntium ;t 'i'tan ate and mixtures thereof,

said ferroelectric material present amoilntsuffi i cient such that the polymeric layerhasa'dielectric I f constant of at least about eight, 1

I 12. The blocking electrode of c'lalm g whereinis aid;

polymeric layer has a dielectric c onstant cof. at least .about 1.5 and is of substantially."uniform thickness within the, range of from about 1 mil to A'inc h'F' 13.;The blocking electrode of claim 12' wherein said gconducti've support'comprises a cylinder orf'continuous "belt hay'in gsaid polymeric layer wrapped'aroun'd the ei(te"r nal periphery thereof, the thickness of said polyme-rs and mixtures thereof;

fthepolymericlmaterial.

l5 'i'Tli'e blocking electrodeof claim 11 wherein the l I ferroelectiici niaterial;is barium titanatelhaving a parti- -cle si ze-yl ithin/the range of about 0.1- to 'l( microns, isaid'bariuni titana't e present at a level of from about 20 

1. A BLOCKING ELECTRODE FOR USE IN A PHOTELECTROPHORETIC IMAGING PROCESS COMPRISING: A. A CONDUCTIVE SUPPORT HAVING MEANS FOR COUPLING TO AN ELECTRICAL ENERGY SOURCE; B. A POLYMERIC LAYER IN CONTACT WITH SAID CONDUCTIVE SUPPORT; SAID POLYMERIC LAYER COMPRISING A POLYMERIC MATERIAL HAVING FROM ABOUT 20 TO ABOUT 90 PERCENT BY WEIGHT OF A FINELY DIVIDED FERROELECTRIC MATERIAL DISPERSED THEREIN, SAID FERROELECTRIC MATERIAL HAVING A DIELECTRIC CONSTANT OF AT LEAST ABOUT
 15. 2. The blocking electrode of claim 1 wherein said polymeric layer is adapted for interposition between the conductive support and a second electrode.
 3. The blocking electrode of claim 2 wherein said ferroelectric material is selected from the group consisting of alkaline earth metal titanates and alkaline earth metal stannates.
 4. The blocking electrode of claim 3 wherein said polymeric layer is in the form of a sheet adapted for feeding between said conductive support and said second electrode.
 5. The blocking electrode of claim 3 wherein said conductive support comprises a cylinder or continuous belt having said polymeric layer wrapped about the external periphery thereof.
 6. The blocking electrode of claim 5 wherein said polymeric material comprises a cured elastomer.
 7. The blocking electrode of claim 6 wherein said polymeric layer has a dielectric constant of at least about 15 and a volume resistivity within the range of about 108 to 1012 ohm-cm.
 8. The blocking electrode of claim 7 wherein the polymeric layer further contains from about 0.1 to about 25 percent by weight of a conductive material having a volume resistivity of less than about 106 ohm-cm.
 9. The blocking electrode of claim 8 wherein said conductive material comprises carbon black.
 10. The blocking electrode of claim 6 wherein the cured elastomer is selected from the group consisting of butadiene/acrylonitrile rubber, chlorosulfonated polyethylene, epichlorohydrin polymers and mixtures thereof.
 11. A blocking electrode for use in a photoelectrophoretic imaging process comprising: a conductive support having means for coupling to an electrical energy source; a polymeric layer in contact with said conductive support and interposed between said conductive support and a second electrode; said polymeric layer comprising a uniform mixture of a polymeric material having a volume resistivity of greater than about 107 ohm-cm and a finely divided ferroelectric material selected from the group consisting of barium titanate, strontium titanate and mixtures thereof, said ferroelectric material present in an amount sufficient such that the polymeric layer has a dielectric constant of at least about eight.
 12. The blocking electrode of claim 11 wherein said polymeric layer has a dielectric constant of at least about 15 and is of substantially uniform thickness within the range of from about 1 mil to 1/4 inch.
 13. The blocking electrode of claim 12 wherein said conductive support comprises a cylinder or continuous belt having said polymeric layer wrapped around the external periphery thereof, the thickness of said polymeric layer being at least about 5 mils.
 14. The blocking layer of claim 13 wherein said polymeric material is a cured elastomer selected from the group consisting of butadiene/acrylonitrile rubber, chlorosulfonated polyethylene, epichlorohydrin polymers and mixtures thereof.
 15. The blocking electrode of claim 11 wherein the ferroelectric material is barium titanate having a particle size within the range of about 0.1 to 10 microns, said barium titanate present at a level of from about 20 to 90 percent by weight of the polymeric material. 